Digital microcells for cellular networks

ABSTRACT

A cellular telephone system is described of the type wherein a plurality of contiguous cells, each having an assigned set of identification codes, are arranged with means for maintaining continuous communication with mobile telephones moving from cell to cell. The system allows multiple access by including means for assigning at least one of the in the assigned set of identification codes to more than one mobile telephone. A unique identification code is assigned to a mobile telephone located in the cell. A signal having a unique identification code is generated for identifying the mobile telephone. The signal is coupled to the zones. A combiner is also provided for combining signals from all of the zones in the cell. A receiver is coupled to the combiner for retrieving the signals having the code. According to another aspect of the invention, the signal coupled to the zones is delayed so that the transmission of the signal among the plurality of antenna sets is delayed by a preselected amount so as to reduce interference caused by successive reception of signals.

This is a continuation of application Ser. No 08/263,129, filed Jun. 21,1994 now U.S. Pat. No. 5,504,936, which is a continuation of applicationSer. No. 08/052,636, filed Apr. 26, 1993 now abandoned, which is acontinuation-in-part of application Ser. No. 07/679,521, filed Apr. 2,1991, now U.S. Pat. No. 5,243,598 which applications are incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates generally to cellular telephone systems. Moreparticularly, the invention relates to a digital multiple accesscommunication system for cellular telephone systems.

BACKGROUND OF THE INVENTION

In a typical analog cellular telephone system, a plurality of contiguouscells, each having a different assigned set of transmission frequencies,are arranged with handoff means for maintaining continuous communicationwith mobile telephones moving from cell to cell. As a mobile unittravels along a path that passes from one cell to another, a handoffoccurs which switches the mobile unit from a frequency in the setassigned to the cell it is leaving, to a new frequency in the setassigned to the cell it is entering. The handoff action is controlled bya mobile telephone switching office (MTSO) which receives a handoffcommand or instruction. The handoff command is typically generated whenthe signal received from the mobile telephone falls below a preselectedsignal strength thus indicating that the mobile telephone is at the cellboundary.

In an analog system, each cell in a cellular telephone system operateswith a different assigned set of transmission frequencies. As a mobiletelephone passes from one cell to another, the handoff signal instructsthe cell which the mobile telephone is entering to begin transmitting ata frequency which is different from the frequency which was beingtransmitted by the cell which the mobile telephone was leaving. Asimilar procedure is followed when the mobile telephone passes into thenext contiguous cell. Sets of assigned frequencies are different foradjacent cells, and such sets are not repeated except for cells that arefar enough away from each other so that interference problems will notoccur. In the case of systems using identification codes, theidentification codes are generally not repeated.

A mobile telephone unit typically contains a control unit, atransceiver, and an antenna system. Each cell site typically is providedwith a control unit, radio, a power plant, data terminals, and antennas.The MTSO provides coordination for all the cell sites and containssuitable processing and switching means. The MTSO also interfaces withthe telephone company zone offices for standard hardwired telephonesystems. The communication links between the MTSO and the various cellsites are typically microwave, T carriers, or optical fiber, and carryboth voice and control data between the cell sites and the MTSO.

When a user sitting in a car activates the receiver of the mobile unit,the receiver scans a plurality of set-up channels which are designatedamong the total channels assigned to the cell. Typically, there may be21 set-up channels out of a total of 416 channels. (The remainder arecommunication channels.) The receiver then selects the strongest set-upchannel and locks on for a certain time. Each site is assigned adifferent set-up channel. Accordingly, locking onto the strongest set-upchannel usually means selecting the nearest cell site. Thisself-location scheme is used in the idle stage and is user-independent.It has a great advantage because it eliminates the load on thetransmission at the cell site for locating the mobile unit. Thedisadvantage of the self-location scheme is that no location informationof idle mobile units appears at each cell site. Therefore, when the callinitiates from a standard non-mobile or land line to a mobile unit, thepaging process is longer. Since a large percentage of calls originatesat the mobile unit, the use of self-location schemes is justified. Aftera delay, for example, one minute, the self-location procedure isrepeated.

To make a call from a mobile unit, the user places the called numberinto an originating register in the mobile unit, checks to see that thenumber is correct, and pushes a "send" button. A request for service issent on a selected set-up channel obtained from a self-location schemeas described above. The cell site receives it, and in directional cellsites, selects the best directive antenna for the voice channel to use.At the same time the cell site sends a request to the MTSO via ahigh-speed data link. The MTSO selects an appropriate voice channel forthe call, and the cell site acts on it through the best directiveantenna to link the mobile unit. The MTSO also connects the wire-lineparty through the telephone company central office.

When a land-line party dials a mobile unit number, the telephone companycentral office recognizes that the called number is mobile and forwardsthe call to the MTSO. The MTSO sends a paging message to certain cellsites based on the mobile unit number and a suitable search algorithm.Each cell site transmits the page on its own set-up channel. The mobileunit recognizes its own identification on a strong set-up channel, locksonto it, and responds to the cell site. The mobile unit also follows theinstruction to tune to an assigned voice channel and initiate an audiblesignal to alert the user to the incoming call.

When the mobile user is finished with the call, the hang up turns offthe transmitter, and a particular signal (signaling tone) transmits tothe cell site and both sides free the voice channel. The mobile unitresumes monitoring pages through the strongest set-up channel.

During a call, two parties are on a voice channel. When the mobile unitmoves out of the coverage area of a particular cell site, the receptionbecomes weak. The present cell site requests a handoff via anappropriate signal, for example, a 100 ms burst on the voice channel.The system switches the call to a new frequency channel or a differentcell identification code in a new cell site without either interruptingthe call or alerting the user. The call continues as long as the user istalking. The user does not notice the handoff occurrences.

When call traffic in a particular area increases, increased capacity maybe generated by reducing the area covered by a particular cell, i.e.,creating a microcell. For example, if a cell is split into four smallercells, each with a radius of one-half the original, traffic is increasedfour fold. Naturally, the smaller the cell, the more handoffs requiredin a cellular telephone system for a given capacity.

Although in the proper circumstances, reduced cell size is advantageous,certain problems can arise. Very often when cell size is reduced, forexample to a radius of less than one mile, very irregular signalstrength coverage will result. This may be caused by buildings and otherstructures, and can therefore become highly dependent upon the locationof the mobile unit. Other problems arise in connection with signalinterference. Although some cellular telephone systems have employedseveral sets of frequencies in a small single cell, in an attempt toimprove capacity in that cell, this prevents the reuse of the samefrequencies or adjacent frequencies in the neighboring cells. Theoverall capacity of the system thereby decreases, since the number ofavailable channels in a system is proportional to the inverse of thenumber of different frequency sets employed.

A cellular telephone system in which an antenna set configuration leadsto a more uniform signal coverage contour and lowered interferencelevels is described in U.S. Pat. No. 4,932,049 issued to Lee. Thecellular telephone system comprises cells which contain a plurality ofantenna sets arranged and configured to limit propagation of signalssubstantially to one of a plurality of zones or sectors within theboundaries of the cells. The zones or sectors are substantially less inarea than the area of the cell. Transmission at any one frequency (ofthe assigned set of transmission frequencies for the cell) is confinedto the zone or sector wherein the mobile telephone has been assigned tosuch one frequency. Frequency handoff occurs while the mobile unit movesto a different cell.

In order to optimize the usage of the assigned set of transmissionfrequencies in a zoned or sectored cell described above, multiple accessschemes allowing more than one user to use a communication channel couldbe implemented in the cell. Multiple access is possible because mostusers of a voice communication system do not fully utilize the capacityof the communication system. More specifically, a typical user who isallocated a channel in the communication system only actively uses thevoice channel for a fraction of its allocated time. As an example, atypical user using a voice channel generally speaks for half of the timeand listens for the remaining times. Thus the communication channel isthen left unused for at least half of the time. By appropriateidentifying by user time slot or code, bursts or pockets of voicesignals for different users in digital systems may be transmittedthereby increasing the user capacity of the system.

Analog multiple access schemes such as analog frequency divisionmultiple access have been implemented in cellular telephone systems.Digital multiple access schemes including digital frequency divisionmultiple access, time division multiple access, and code divisionmultiple access have been developed, and it is anticipated that theywill also be implemented in cellular telephone systems. It isadvantageous to implement a multiple access scheme using digital means.This is because digital communication typically offers betterperformance, higher capacity, and lower cost. It should be noted thatthe applications of digital communication are not limited tocommunicating digital data. Analog voice signal can enjoy the benefitsof digital communication by first converting the analog voice signal toa digital signal before transmission. After the digital signal isreceived by a receiver, the digital signal is then converted back to theanalog voice signal.

One of the reasons for the improved performance in a digitalcommunication system is that the system is more tolerant to noise. Thisis because a threshold level of noise energy is required to change thestate of a digital signal. Thus, the communication is relatively errorfree if the noise energy of the communication medium is below therequired level. In addition, it is possible to implement error detectionand correction algorithms which further reduce the error rate even ifthe communication medium is relatively noisy. As a result, it ispossible to set up communication channels under noisy environmentthereby increasing the capacity of the communication system.

Another reason for the improved performance is that digital data can beeasily manipulated using digital processors. Thus, many operations whichare difficult to implement using analog means can be implemented usinglow cost microprocessors and digital logic circuits.

SUMMARY OF THE INVENTION

In accordance with the invention, an improved cell configuration leadsto a more uniform signal coverage contour, lowered interference levels,increased capacity, improved voice quality, and relatively simple andeconomical construction. The improved cell includes a master site and aplurality of zone sites. The improved cell also includes a plurality ofantenna sets, each set being suitably positioned within the periphery ofthe cell to cover a corresponding zone and having transmitting andreceiving means directionally configured to limit propagation of signalssubstantially to a zone within the boundaries of the cell.

In the CDMA system according to the present invention, a uniqueidentification code is assigned to a mobile telephone located in thecell. A signal having a unique identification code is generated foridentifying the mobile telephone. The signal is coupled to the zones. Acombiner is also provided for combining signals from all of the zones inthe cell. A receiver is coupled to the combiner for retrieving thesignals having the code. According to another aspect of the invention,the signal coupled to the zones is delayed so that the transmission ofthe signal among the plurality of antenna sets is delayed by apreselected amount so as to reduce interference caused by successivereception of signals by the mobile telephone located in the cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a typical layout of a cellemployed in the invention.

FIG. 2 is a schematic diagram illustrating another layout of a cellemployed in the invention.

FIG. 3 is a schematic block diagram of the electronics of an embodimentof the present invention.

FIG. 4 is a schematic block diagram of a zone select transmitter systemaccording to the present invention.

FIG. 5 is a schematic block diagram of an embodiment of a zone siteselector according to the present invention.

FIG. 6 is a schematic block diagram of another embodiment of a zone siteselector according to the present invention.

FIG. 7 is a schematic block diagram of a scanning receiver systemaccording to the present invention.

FIG. 8 is a schematic of a master site according to the presentinvention wherein set up channel is transmitted and received throughzone sites.

FIG. 9 is a schematic diagram illustrating a typical layout of a cell ina code division multiple access (CDMA) system according to the presentinvention.

FIG. 10 is a schematic block diagram of the electronics in a CDMA systemaccording to the present invention.

FIG. 11 is a schematic block diagram of the CDMA system including adelay module according to the present invention.

DETAILED DESCRIPTION OP THE INVENTION

There are three main types of digital multiple access systems: digitalfrequency division multiple access (digital FDMA), time divisionmultiple access (TDMA) and code division multiple access (CDMA). Thepresent invention allows the implementation of digital FDMA, TDMA, andCDMA in a microcell. Thus, the benefits of digital multiple accesscommunication can be realized in the microcell. In addition, the presentinvention relating to the digital frequency division multiple access canalso be applied to an analog frequency division multiple access systemby a person of ordinary skill in the art.

Frequency division multiple access, both analog and digital is a methodwhereby the bandwidth of a communication channel is subdivided infrequency into subchannels so that more than one user can use thecommunication channel simultaneously.

TDMA is a method whereby the time of operation of a communication systemis divided into a plurality of time slots having predetermined lengths.The system transmits information relating to a user only during the timeslots assigned to the user. The system has means to temporarily storeinformation generated by the user during other times so that informationis not lost during these times. Thus, more than one user is able to usethe same channel in the communication system.

In a preferred cellular TDMA system, the bandwidth of a channel is 30KHz. Three callers have access to a particular channel. Communicationtime is divided into time frames of 20 ms and the time frames aredivided into three slots of 6.66 ms each. Each mobile unit is assignedone of the three time slots in a particular channel.

CDMA is a method whereby each user is assigned a different coding schemeinstead of being assigned a different frequency channel or a differenttime slot. These coding schemes are orthogonal or partially correlatedto each other so that it is possible to identify the user based on ananalysis of the codes used in the transmission. As a result, more thanone user can use the same channel.

CDMA is especially desirable if the communication channel is relativelynoisy. This is because CDMA typically uses spread spectrum techniqueswhich are known to be tolerant to noise and multipath interference. As aresult, CDMA allows more users to use the noisy channel to make initialcalls thereby increases the capacity of the channel.

Another advantage of CDMA is that every cell uses the same set of wideband frequencies, or channels. As a result, it is possible to have theclosest co-channel separation, i.e., the ratio of the co-channelseparation distance (D) and the cell radius (R) in a CDMA system couldbe equal to 2, whereas the ratio D/R for other communication methods isabout 4.6.

A consequence of using the same set of wide band frequencies in everycell is that no frequency switching is required as mobile units movefrom cell to cell. Instead, the coding scheme in CDMA has a code foridentifying the cells. As mobile units move from cell to cell, only theidentification codes for the cells need to be changed. Such change inthe identification code instead of changing frequency is referred to as"soft" handoff. As a result, the performance of the system improves.

An example of a microcell in which the system according to the presentinvention can be used is shown in a cell 1 of FIG. 1. The structure ofcell 1 is disclosed in U.S. Pat. No. 4,932,049 issued to Lee, which isincorporated herein by reference. This structure leads to a more uniformsignal coverage contour and lowered interference levels.

The outer boundary of cell 1 is delineated by the circle 11 in solidline. Although shown as a circle, cells are often represented ashexagons in designed illustrations. In reality, however, due to theshape of terrain and the presence of buildings and other structures, theactual boundary of the circle 11 may be of an irregular shape. In anycase, the solid line 11 is intended to represent that location at whicha mobile telephone unit passes from the influence of the illustratedcell and into the influence of an adjacent cell.

Three separate antenna sets 13, 15, and 17 are positioned within cell 1.Antenna set 13 is located at a zone site 14, whereas antenna sets 15 and17 are located at zone site 16 and 18, respectively. One of the zonesites, for example, zone site 14, can collocate with a master site whichprocesses the signal to and from the zone sites. Depending upon theparticular conditions within the cell area, other numbers of antennasets may be usefully employed, and it is to be understood that the useof three sets in FIG. 3 is for illustrative purposes only. Each antennaset includes a transmitting antenna 13a, 15a, and 17a, respectively.Each antenna set also includes two receiving antennas 13b and 13c, 15band 15c, and 17b and 17c, respectively. Duplication of the receivingantennas at each zone site is for diversity use to reduce signal fadingby combining the signals. The determination of the locations of zonesites and the number of zone sites in a cell can be based on the Lee'scoverage prediction model published in IEEE Transactions on VehicularTechnology, February, 1988.

Each antenna set has its own zone of major influence for transmittingand receiving signals. Thus, antenna set 13 at the master site 14 has azone indicated by the dotted line 13z. Similarly, antenna set 15 at zonesite 16 has a zone of influence designated by the dotted line 15z andantenna set 17 at the zone site 18 has a zone of influence designated bythe dotted line 17z. It may be seen from FIG. 1 that the zones overlapin certain areas. Directionality is provided to the antenna sets so thatthe zones of influence, i.e. the zones of propagation and reception ofsignals, are limited to be substantially within the boundaries ofcell 1. Such directionality is provided by suitable means such as shownas a symbolic means 19 arranged at each antenna set or zone site. Thedirectionality means 19 can be a reflector for each individual antenna,or any other suitable arrangement to provide the desired directionalityand coverage.

The signal of the set up channels can be communicated to the mobileunits inside cell 1 in two different configurations. The firstconfiguration uses an additional antenna set in the master site, in thiscase, zone site 14. Thus, antenna set 13 includes a setup transmittingantenna 13d for transmitting set up signals, and duplicate setupreceiving antennas 13e and 13f for receiving set up signals, as will beexplained below. The set of setup antennas 13d, 13e and 13f, however, isconfigured to have a greater zone of influence, this being indicated bythe dash-dot line 21, substantially coextensive with the limits of cell1 delineated by circle 11. The second configuration uses the same setsof antenna 13a-c, 15a-c, and 17a-c for communicating both the voicechannel and set up channel. In this configuration, no additional antennaset is required.

FIG. 2 is another example of microcell 110 in which the system accordingto the present invention can be used. Microcell 110 is preferablypositioned along a highway 150 for providing cellular telephone servicesto mobile units (not shown) moving along highway 150. Microcell 110comprises a plurality of zones, illustrated by the dotted circles113-116. It is to be understood that the number of zones in FIG. 2 andthe shape of the zones are for illustrative purposes only. Each zonecomprises a zone site for housing at least one antenna set. Thus zones113-116 comprises zone sites 123-126 and antenna sets 133-136. One ofthe zone sites can also be a master site.

The advantage of microcell 110 is that a long stretch of highway 150 canbe covered by a set of assigned frequencies. Thus, a mobile unit cantravel a long distance without the need for a handoff action. INaddition, the power radiated by antennas 133-136 could be low and stillcover the stretch of highway because the area of each zone is small. Asa result, the microcell 110 could be implemented using low costequipment.

FIG. 3 shows a block diagram of the electronics which can be used eitherin a TDMA or in a digital FDMA located in the cell of FIG. 1. Two zonesites 16 and 18 are each coupled to a master site 14 and are controlledtherefrom. In the illustrated embodiment, zone site 16 is connected tomaster site 14 via three cables 23, 25, and 27. Zone site 18 isconnected to master site 14 via cables 29, 31, and 33. The specificnature of the signals assigned to the respective cables will bedescribed below. Generally, however, cables 23 and 29 carry transmitterantenna signals whereas cables 25, 27, 31, and 33, carry receiverantenna signals. The illustrated embodiment depicts the communicationbetween the zone sites and the master site as being via cable. It willbe apparent to those skilled in the art that such cables may include,for example, T1 carrier cables, optical fibers, or the like. The cablesmay also be replaced by microwave channels.

The zone sites each contain a signal processing ensemble of componentsas shown at 35 for zone site 14a. It is understood that substantiallyidentical signal processing ensembles are contained in zone sites 16 and18, although such ensemble are not shown in FIG. 3 for simplicity.Signal processing ensemble 35 includes a filter 37, an amplifier 39, anda converter 41 interposed between antenna 13a and output cable 43.Similarly, filter 45, amplifier 47, and converter 49 are interposedbetween antenna 13b and output cable 51, and filter 53, amplifier 55,and converter 57 are interposed between antenna 13c and output cable 59.The filters, amplifiers, and converters filter, enhance, and convertsignals as desired and may be of any type suitable for the statedpurpose.

In FIG. 3, the three amplifiers 39, 47, and 55 enhance the UHF signalsapplied to their input from filters 37, 45, and 53 respectively. TheseUHF signals are then applied to converters 41, 49 and 57, which eitherup convert or amplitude modulate the frequency to an optical frequency,where optical fibers are used for the cable connections, or down convertthe frequency to a base band for passing through T1 carrier cables. Theymay also directly convert from UHF to microwave where microwave channelsare used. The filters, amplifiers and converters may be of any typesuitable for the stated purpose.

Master site 14 comprises a zone selector 95, a transmitter module 96, areceiver module 97, a controller 98, and a set up channel 99. Controller98 communicates with the MTSO. Transmitter module 96 comprises aplurality of transmitters. Each transmitter generates a signal having afrequency corresponding to the assigned frequency of a channel. Thesignals generated from the transmitters in transmitter module 96 iscoupled to the appropriate zone site through zone selector 95 forcommunication with the mobile units. Zone selector 95 also receivessignals from the three zone sites, and, after processing these signalsin a manner described below, couple the signal to receiver module 97.Receiver module 97 comprises a plurality of receivers for recovering thesignals generated by mobile units in the cell. Each receiver is atwo-branch diversity receiver, well known in the art, which comprisestwo inputs, each input accepting a signal from one of the two receivingantenna in the zone site. Each receiver is tuned to a frequencycorresponding to the assigned frequency of a channel. The recoveredsignals are coupled to controller 98.

Zone selector 95 comprises a zone switch 92, a zone switch/combiner 94,and a zone scanner 93. Zone switch 92 receives signal from transmittermodule 96 and directs the signal to the appropriate zone site forcommunication with the mobile units. An exemplary implementation of zoneswitch 92 is shown at FIG. 4. The selection of the appropriate zone siteis determined by a selection signal generated by zone scanner 93. Anexemplary implementation of zone scanner 93 is shown at FIG. 7. Zoneswitch/combiner 94 receives signal from the zone sites, and, dependingon the mode of operations, described below, either combines the signalsfrom the three zone sites or selects a signal from one zone beforecoupling the resulting signal to receiver module 97. Exemplaryimplementations of zone switch/combiner 94 are shown at FIGS. 5 and 6.

At master site 14, the output ports 71-73 of zone switch 92 go throughconverters 61-63, respectively, and then coupled to zone sites 14a, 18and 16, respectively, through cable connectors 43, 29, and 23,respectively. The selection of the appropriate zone site is determinedby a selection signal generated by a zone scanner which is input to zoneswitch 92 through an input port 87. Zone switch 92 also has an inputport 88 for inputting a set of transmitting signals generated bytransmitter module 96.

Zone scanner 93 comprises three input ports 81-83 for coupling signalsfrom the three zone sites via converters 64-66, respectively. Thestrength of these signals are compared to determine the zone site whichgives rise to the strongest signal. Alternatively, the zone site canalso be selected based on the supervisory audio tone (SAT) signal. Zonescanner 93 also comprises an input port 85 for accepting a time divisionclock signal from receiver module 97 for separating the appropriate timeslot. The selection signal generated by zone scanner 93 is sent to anoutput port 84 for coupling to zone switch/combiner 94 and zone switch92.

The signal received from the three zone sites, after going through cableconnectors 25, 27, 31, 33, 51, 59, and converters 64-69, terminates atthe input ports 74-79 of zone switch/combiner 94. If zoneswitch/combiner 94 operates in a zone switching mode, a selection signalis coupled to an input port 89. The selection signal selects one of thesignals from one of the three zone sites for coupling to the outputports 90, 91. If zone switch/combiner 94 operates in a combing mode suchthat the signals from all the zones are combined, the selection signalis not used. Zone switch/combiner 94 generates two sets of outputsignals, one at an output port 90 and the other at an output port 91.Each member of each set of output signals is coupled to a correspondinginput terminal of a two-branch diversity receiver in receiver module 97.

It can be understood by a person of ordinary skill in the art that ifmaster site 14 is co-locate with one of the zone site, say zone site14a, no converter is required for communicating between master site 14and the co-located zone site 14a. In this case, converters 41, 61, 49,64, 57, and 67 are not needed.

Controller 98 measures the signal strength of a channel requested by theMTSO. If the initial call is in this particular cell, or if the call ishanded off to this particular cell through the controller, thecontroller initiates one of the transmitters in transmitter module 96 totransmit at a particular frequency assigned by a MTSO to that call. Thesignal is then sent to a proper zone through zone switch 92. If duringthe call, the signal strength received at controller 98 is below apreselected level, the controller initiates a handoff process from theMTSO to handoff the call to another cell.

In FIG. 3, controller 98 is connected to a set up channel 99 whichtransmits and receives signals on the three control antennas 13d, 13e,and 13f. The set up channel assigned in each cell can cover the entirezone of influence 21, shown in. FIG. 1, which is coextensive with cell 1in FIG. 1. However, it is also possible to transmit the set up channel99 to each zone site so that no setup channel antennas are needed. Inthis case, all zone sites transmit and receive the setup channel insideits zone of influence. An exemplary setup channel which does not usesetup channel antenna is shown in FIG. 8.

In operation of the system above described, a mobile unit which isoperating on an assigned frequency f₁ in the cell will typically bemoving within the cell. All zone sites within the cell will receivesignal levels (strengths), but only that zone site at which the receivedsignal level is the strongest will transmit and receive signals to themobile unit during a call. The transmitters in the other zone sites donot transmit to the mobile unit. When the mobile unit moves such thatthe received signal strength at a zone site other than the one that iscurrently transmitting becomes strongest, the system operates to turnoff the transmitter at the weaker zone site and turn on the transmitterat the zone site at which the stronger signal level is being received.The two-diversity antenna signal at each zone are also selected from theproper zone site to receive the call. The operating frequency, however,remains unchanged at f₁. Thus, no handoff has occurred in thetraditional sense and the MTSO is not involved. As a result, noadditional handoff load is added to the MTSO switching equipment. Analternative way is to combine the two diversity antenna signals from allzones, as described below.

As was noted above, the block diagram shown in FIG. 3 can be used bothin digital FDMA and TDMA. In a TDMA scheme, a plurality of time divisionmultiplexers and an associated synchronization clock is used, asexplained below. In a digital FDMA scheme, it is not necessary to usethe time division multiplexers and the associated clock.

FIG. 4 shows a block diagram of an exemplary zone switch, shown asnumeral reference 92 in FIG. 3, according to the present invention. Zoneswitch 200 comprises two input port 283, 285 and three output ports211-213 which correspond to ports 87, 88, and 71-73, respectively, ofzone switch 92 in FIG. 3. Thus, signals from a transmitter module, shownas 96 in FIG. 3, is coupled to input port 285 of zone switch 200. Thesesignals are directed by zone switch 200 to the three zone sites 14a, 18,and 16 through output ports 211-213.

As was noted above, transmitter module 96 comprises a plurality oftransmitters, each generating a different signal. Thus, Input port 285further comprises a plurality of input terminals, shown as 286 and 287in FIG. 4. Terminal 286 couples a signal having a frequency of f₁ intozone switch 200 and terminal 287 couples a signal having a frequency off₂ into transmitting zone switch 200.

Zone switch 200 further comprises a plurality of time divisionmultiplexers, two of them, 251 and 261 are shown at FIG. 4 forillustrative purpose. In general, the number of time divisionmultiplexers is the same as the number of frequency channels assigned tothe cell. Zone switch 200 also comprises a plurality of channel zoneswitches, six of them, 241-246, are shown at FIG. 4. In general, thenumber of zone switches is equal to the product of the number of timeslots and the number of time division multiplexers. Zone switch 200further comprises three combiners 221-223, one associated with each zonesite, for combining the signals from the channel zone switches forsending to the three zone sites.

A time division multiplexer (TDM) is a device, well known in the art,for dividing time intervals into time slots. In FIG. 4, TDM 251 and 261divide each time interval into three time slots. Preferably each timeslot is 6.66 ms long in a 20 ms time interval. It may be understood thata TDM can divide time intervals into any suitable number of time slots,and the choice of the number of divisions in TDM 251 and 261 are forillustrative purposes only.

TDM 251 comprises an input port 253 for accepting signals having afrequency of f₁, generated by a transmitter of transmitter module 96,shown in FIG. 3. The time interval for transmitting the signal havingfrequency f₁ is divided into three time slots. The signals of the timeslots are coupled to output ports 256-257. Each of these signals iseventually directed to a zone site for communicating with a mobile unit.Since different time slots can be directed to different zone sites, itis possible that three mobile units in three zone sites communicate withmaster site 14 using the same frequency channel.

Similarly, TDM 261 comprises an input port 263 and three output ports266-268. Ports 263 and 266-268 correspond to ports 253 and 256-258,respectively, of TDM 251. TDM 261 functions in a similar way as TDM 251.All the output signals from TDM 261 have frequency f₂ since the inputsignal to TDM 261 has a frequency of f₂. Again, signals having frequencyf₂ in the three time slots can be directed to the same or different zonesites.

Each of the output ports from the TDMs is coupled to a channel zoneswitch for directing the output of a communication channel from the TDMsto the appropriate zone site. Thus, output ports 256-258 and 266-268 arecoupled to channel zone switches 241-246, respectively. The constructionof all the channel zone switches are substantially the same. Thus, onlyone channel zone switch, 241, is described in detail.

Channel zone switch 241 comprises, an input port 231 for acceptingsignals from TDM 251. Channel zone switch 241 also comprises threeoutput ports 235-237 coupled to combiners 221-223, respectively, fordirecting signals to one of the three combiners. Channel zone switch 241further comprises a switch 233 for selectively coupling the input port231 to one of the three output ports 235-237. The coupling is controlledby a selection signal at a control port 232. Control port 232 is coupledto input port 283. As was noted above, input port 283 corresponds toport 87 in FIG. 3 which is coupled to zone scanner 93. Depending on thestatus of the signal at input port 232, the signals from output port 256of TDM 251 could be sent to one of the three zone sites.

Similarly, each channel zone switch has three output ports for couplingto the three combiners. Again, depending on the status of the controlport, the outputs of the channel zone switch is coupled to one of thethree combiners. Each of the combiners 221-223 combines all the signalscoupled thereto and sends the signals out to the zone sites throughoutput ports 211-213, respectively.

As was noted above, a typical TDMA system divides a time interval of 20ms into time slots. If quadruture phase shift-keying modulation is used,a total of 486 symbols can be transmitted within the 20 ms timeinterval, i.e., the time duration for each symbol is 41 microseconds. Inorder to ensure that the last symbol of one slot and the first symbol ofthe next slot are correctly received, the rate of switching should befaster than the time duration for a single symbol, i.e., 41microseconds. In order to prevent undesirable effects resulting fromswitching transients, a TDM switch which has a switching ratesubstantially faster than 41 microseconds should be used. Examples ofsuch TDM switches are part numbers 54F/74F 151A manufactured by NationalSemiconductor and 10G050A manufactured by GBL.

It should be noted that the block diagram shown in FIG. 4 can also beused in a digital FDMA scheme if the TDMs are removed from the blockdiagram. In this case, the signals from the transmitters in transmittermodule 96, shown in FIG. 3, are coupled directly to the channel zoneswitches, and the number of channel zone switches are the same as thenumber of transmitters instead of three times the number of transmittersif the TDMs are included. Thus, terminal 286 couples a signal havingfrequency f₁ to one of the three channel zone switches 241-243.Similarly, terminal 287 couples a signal having frequency f₂ to one ofthe three channel zone switches 244-246.

FIG. 5 is a block diagram of a zone switch/combiner 300 according to thepresent invention. In this embodiment, zone switch/combiner 300 operatesas a combiner and will be referred to as zone combiner in the followingdescription of FIG. 5. The block diagram in FIG. 5 also includes areceiver module 330. Zone combiner 300 and receiver module 330correspond to zone switch/combiner 94 and receiver module 97 in FIG. 3.

Zone combiner 300 comprises seven input ports 303, 304-309, and twooutput ports 301, 302. Input ports 303, 304-309 and output ports 301,302 correspond to input ports 89, 74-79 and output ports 90, 91,respectively, of FIG. 3. Thus, the signals at input ports 304-309 aresignals from the zone sites.

The signals from input ports 304-306 are combined by combiner 321 andcoupled to output port 301. Since input ports 304-306 are coupled to thezone sites, it means that all three signals from all the three zonesites are combined together by combiner 321. Similarly, the signals frominput ports 307-309 are combined by combiner 321 and then coupled tooutput port 302. Again, input ports 307-309 are coupled to the threezone sites, thus, the three signals from the three zone sites arecombined together by combiner 321. The signals at output ports 301 and302 are coupled to receiver modules 330 in an arrangement describedbelow. Since there is no need to select the zone sites in thisembodiment, the select signal present at port 303 is not used.

Receiver module 330 comprises a plurality of two-branch diversityreceivers, only three of these receivers, 333, 335, 337, are shown inFIG. 5. These receivers 333, 335, 337 are TDM receivers and couldrecover individual signals sent by the mobile units. Each receiver inmodule 311 is tuned to a frequency corresponding to the frequencygenerated by a corresponding transmitter in transmitter module 96, shownin FIG. 3.

Each receiver in receiver module 330 comprises two input ports. One ofthe input ports is coupled to port 301 and the other input port iscoupled to port 302. The recovered signal from each receiver is sent tocontroller 98, shown in FIG. 3. It is well known in the art that thetwo-branch diversity receiver arrangement enhances the quality of thereceived signal.

Since all the receivers in receiver module 330 are TDM receivers, allthe receivers share a common clock (not shown) which can be used forsynchronization with the time slots of the TDMs in zone switch 200,shown in FIG. 4. The common clock signal is sent out of receiver module330 through an output port 340. As was noted above, this clock signal iscoupled to zone scanner 93, shown in FIG. 3, for synchronization.

It should be noted that if the block diagram of FIG. 5 is used in adigital FDMA scheme, no synchronization clock is needed. Consequently,port 341 is not needed.

Zone combiner 300, shown in FIG. 5, is preferably used if thetransmission rate is low, typically less than 10 kilobits per second, orthe distance between the zone sites and the master is short, typicallyless than one half of a kilometer. Otherwise, another implementation ofzone site selector, shown at FIG. 6, should preferably be used.

Even though zone combiner 300 is described as part of a TDMA and adigital FDMA scheme, it should be noted that zone combiner 300 can alsobe used in an analog multiple access system and in a portable telephonesystem. One of the advantages in using zone combiner 300 in an analogsystem is that the power delivered to the receivers in receiving module330 is increased because all the power from the three zone sites areutilized. Another advantage is that temporal loss of received signalfrom one zone would have less effect on the quality of the signalbecause signals from the other zones could compensate for such loss.

FIG. 6 is a block diagram of a receiver module 390 and a zoneswitch/combiner 350 which is suitable for high transmission rates or insituations where the distance between the zone sites and the master siteis long. In this embodiment, zone switch/combiner 350 operates as a zoneswitch, and will be referred to as a zone switch for receiving in thedescription of FIG. 6. Receiver module 390 is similar to receiver module330 of FIG. 5 and comprises a plurality of two branch diversityreceivers 391-393 for recovering signals transmitted by mobile units.Receiver module 390 also comprises an output port 394 for sending aclock signal to zone scanner 93, shown in FIG. 3, for synchronization.

Zone switch 350 comprises two sets of channel zone switches 360 and 365.Zone switch 350 further comprises two output ports 352, 353, and seveninput ports 351, 354-357 which correspond to ports 90, 91, 89, and74-79, respectively, of zone switch/combiner 94, shown in FIG. 3. Inputsignals from input ports 357-359 are coupled to the first set of channelzone switches 360. Input signals from input ports 354-356 are coupled tothe second set of channel zone switches 365.

Each set of channel zone switches 360, 365 has a plurality of channelzone switches, 361-363 and 366-368. The number of channel zone switchesin each set is the same as the number of channels in receiving module390. Each channel zone switch selects one of the zone sites in responseto a control signal at input port 351. Since input port 351 correspondsto port 89 in FIG. 3, the control signal is a signal from zone scanner93, shown in FIG. 3.

The channel zone switches in zone switch 350 for receiving issubstantially the same as the channel zone switches in zone switch 200for transmitting, shown in FIG. 4, except that the channel zone switchesin receiving zone switch 350 have three input ports and one output portinstead of three output ports and one input port. Again, a selectionsignal is used to determine the coupling of the output port to one ofthree input ports. Since the operations of all the channel zone switchesare the same, only one channel zone switch, 361, is described in detail.

Channel zone switch 361 comprises three input ports 371-373 foraccepting signals from input ports 359, 358, and 357, respectively.Channel zone switch 361 also comprises an output port 375 for couplingsignal to a terminal 381 inside output port 353, preferably an outletbox, of receiving zone switch 350. Channel zone switch 361 furthercomprises a switch 376 for selectively coupling the output port 375 toone of the three input ports 371-373. The coupling is controlled by aselection signal at a control port 374. Control port 374 is coupled toinput port 351. As was noted above, input port 351 corresponds to port89 in FIG. 3 which is coupled to zone scanner 93. Depending on thestatus of the signal at input port 375, the signals from one of theinput ports 371-373 of channel zone switch 361 could be sent to outputport 375.

The output signal from channel zone switch 361 is coupled to an inputport of receiver 391. This signal comprises one branch of a two-branchdiversity signal. Similarly, the output from channel zone switch 366 iscoupled to another input port of receiver 391. This signal comprises asecond branch of a two-branch diversity signal. Receiver 391 recoversthe signal transmitted by a mobile unit and sends this signal tocontroller 98, shown in FIG. 3.

Similarly, the output signals from channel zone switches 362, 367 arecoupled to receiver 392 and the output signals from channel zoneswitches 363, 368 are coupled to receiver 393. The signals recovered byreceivers 392, 393 are coupled to controller 98.

It should be noted that if the block diagram of FIG. 6 is used in adigital FDMA system, no synchronization clock is needed. Consequently,port 341 is not needed.

FIG. 7 is an exemplary implementation of a zone scanner 400. Scanningreceiver 400 comprises three frequency scanners 411-413, three time slotswitches 421-423, and a comparator 427. Zone scanner 400 furthercomprises four input ports 437, 431-433 and an output port 439. Ports431-433, 437, and 439 correspond to ports 81-83, 85, and 84,respectively, of zone scanner 93, shown in FIG. 3.

Signals from zone sites 14a, 18, and 16 are coupled to frequencyscanners 411-413 through input ports 431-433, respectively. Frequencyscanners 431-433 scan a predetermined number of frequencies from zonesites 14a, 18, and 16, respectively. Time slot switches 421-423selectively couple one of the three scanners 411-413 to comparator 427at any given time. The timing for coupling one of the three scanners411-413 is controlled by a clock signal input from port 437.

Comparator 427 stores and compares the average signal strength of thesignals from the three zone sites. As a result, it is possible todetermine the zone site which gives rise to the strongest signalreceived at the master site. This information is coupled to output port439 as a selection signal for controlling the zone switches. Comparator427 preferably includes hysteresis means for reducing the ping pongeffects resulting from instantaneous signal fluctuations. Comparator canalso be used to compare the strongest supervisory-audio-tone signalsamong the three zones.

It should be noted that if the block diagram of FIG. 7 is used in adigital FDMA scheme, no synchronization clock and time slot switch isneeded. Consequently, time slot switches 421-423 and port 431 are notneeded.

FIG. 8 is a schematic block diagram of a master site 640 wherein thesetup channel is transmitted and received by the three zone sitesinstead of using setup channel antennas. The zone switch/combiner 94,zone switch 92 for transmitting, zone scanner 93, controller 98, andconverters 61-69 in FIG. 8 function the same and share the same numeralreferences as the corresponding elements of FIG. 3. Consequently, theseelements and their connections are not described here.

Controller 98 is coupled to a set up transmitter 612 which is in turncoupled to a power splitter 614. Power splitter 614 splits the signalgenerated by set up transmitter 612 into three substantially identicalsignals. Each of the three signals is coupled to a correspondingcombiner 616, 618, 620. Signals from the output ports 71-73 of zoneswitch 92 for transmitters are also coupled to combiners 620, 618, and616, respectively. The combined signals from combiners 620, 618, and 616are coupled to converters 61-63 for sending to the corresponding zonesites. A power splitter is used in FIG. 8 because the location of themobile unit is not known during set up operations.

Signals from converters 64-69 are coupled to a combiner 624 in additionto zone switch/combiner 94. Combiner 624 combines the signals fromconverters 64-66 into one signal and couples the combined signal to oneinput port of a two-branch diversity set up receiver 622. Combiner 624also combines the signals from converter 67-69 into one signal andcouples the combined signal to a second input port of receiver 622.Receiver 622 recovers the set up channel transmitted by a mobile unitand couples the signal to controller 98.

Zone switch/combiner 94 can either be of a type comprising a combiner,shown in FIG. 5, or of a type comprising channel zone switches, shown inFIG. 6. If zone switch/combiner 94 comprises a combiner, this combinercan be physically combined with combiner 624.

It should be noted that the arrangement in FIG. 8 can be used in analogfrequency division multiple access, digital frequency division multipleaccess, TDMA, and CDMA.

FIG. 9 is a schematic diagram illustrating a typical layout of a cell500 utilized in a CDMA system according to the present invention. Theouter boundary of cell 500 is delineated by a circle 511 in solid line.The circle is used for illustrative purposes only and the actualboundary of cell 500 may have an irregular shape. Three separate antennasets 521-523, are each positioned in a zone site 516, 514, and 518,respectively, within cell 500. A master site is co-located with a zonesite, in this case, zone site 514. Depending upon the particularconditions within the cell area, other members of antenna sets may beusefully employed.

Each antenna set includes a transmitting antenna 521a, 522a, and 523a.Each antenna set also includes two receiving antennas 521b and 521c,522b and 522c, and 523b and 523c, respectively. Duplication of thereceiving antenna at each sub-site is for diversity use to reduce signalfading by combining the signals. Directionality of the antenna isprovided by suitable means, shown as a symbolic means 519, for each setof antennas. Each antenna set has its own zone of major influence fortransmitting and receiving signals. Thus antenna set 521-523 has zonesof influence designated by dotted lines 531-533, respectively. Incontrast to the antenna arrangement shown in FIG. 1, there is noseparate setup channel antenna.

In the CDMA system according to the present invention, the three zonesites are transmitting and receiving signals continuously. Thus, cell500 becomes a three-zone microcell. Since the radius of each microcellis about half that of the cell, the power level required is reduced by afactor of four. Consequently, the amount of interference to neighboringcells are reduced substantially thereby resulting in higher quality. Inaddition, the reduced power level also allows the use of low costequipment.

FIG. 10 is a schematic block diagram of the electronics of a CDMA systemaccording to the present invention. The functions of the components inFIG. 10 are substantially the same as the functions of the components inFIG. 3, except that zone selector 95, which comprises zone switch 92,zone scanner 93, and zone switch/combiner 94, is replaced by a zoneselector 582, which comprises a combiner 581. The components having thesame functions in FIGS. 3 and 8 are shown with the same numeralreferences, and the functions and connections of these components arenot described here.

The CDMA system, shown in FIG. 10, comprises a transmitter module 573which includes at least one wide-band (spread spectrum) transmitter forgenerating signals having the appropriate codes at the initiation of asignal from a controller 98. The signal generated by module 573 arecoupled to combiner 581. The combined signal is sent to all zone sitesfor the antenna set inside the zone site. Unlike the TDMA system, it isnot necessary to divide time intervals into time slots and select theappropriate zone sites.

Signals received by all the zone sites are also combined by combiner581. Thus, signals received by converters 64-65 are combined by combiner581. The combined signal is sent to one input port of all the two-branchdiversity receivers in a receiver module 575. Similarly, signalsreceived by converters 67-69 are combined by combiner 581 and sent to asecond input port of all the two-branch diversity receivers in receivermodule 575. Receiver module 575 comprises at least one CDMA receiver,well known in the art, for recovering the signals sent by the mobileunits to the master site 514. After the signals coupled to the receiversare diversity combined, they are coupled to controller 98.

Refer now to FIG. 11. FIG. 11 is a schematic block diagram of theelectronics of a CDMA system according to the present invention with theaddition of a time delay module which serves to reduce interferencetimes. The functions of the components in FIG. 11 are substantially thesame as the functions of the components in FIG. 10. The componentshaving the same functions in FIG. 10 are shown with the same numeralreferences, and the functions of these components are not describedhere.

Those skilled in the art will recognize that land-based cellulartransmission experiences signal fading that typically consists of theRayleigh fading component with a direct N component. In the multipletransmitter arrangement of the present invention, there is an areawithin the preferred cell that falls within the zone of influence of allthree antenna sets designated by lines 531-533 in FIG. 9. As a result,multiple signals originating from three antenna sets arrive almostsimultaneously at the mobile receiver from many directions with manydifferent transmission delays. In most situations, the delay between thereceived signals will be large enough to allow a correlator, of aconstruction well-known to those skilled in the art (not shown), todifferentiate among and combine the signals. However, as the size of thecell shrinks, the delay between the signals becomes too small to allowthe correlator to function properly. At the UHF frequency bands usuallyemployed for mobile radio communications, including those of cellularmobile systems, significant phase differences in signal traveling ondifferent paths may occur. The possibility for destructive summation ofsignals may result.

In a CDMA cellular telephone system, high modulation allows manydifferent production paths to be separated, provided the difference inpath propagation delays exceed the modulation chip duration, or onebandwidth. As an example, when pseudo noise (PN) modulation is employedas the preferred modulation means, if a PN chip rate of one MHz is used,the full spread spectrum processing gain, equal to the ratio of thespread bandwidth to the system data rate, can be employed against pathsthat differ by more than one microsecond in path delay from the desiredpath. A microsecond path delay differential corresponds to differentialpath distance of 1,000 feet. The urban environment typically providesdifferential path delays in excess of one microsecond, and up to 1-20microseconds are reported in some areas.

In the instant invention, the signal transmitted by each antenna set ispreferably a direct sequence spread spectrum signal modulated by a PNsequence clock at a predetermined rate, which in the preferredembodiment is 1.25 MHz. A property of the PN sequence as used in thepresent invention is that discrimination is provided against multi-pathsignals. When the signal arrives at the mobile receiver after passingthrough more than one path, there will be a difference in reception timeof the signals. This reception time difference corresponds to thedifference in distance divided by the speed of light. If this timedifference exceeds one microsecond, then a correlation process can beemployed to discriminate against one of the paths.

As discussed above, however, smaller cell size decreases the receptiontime difference. In order to ensure an initial time difference in excessof one microsecond between each of the three signals being transmittedfrom the exemplary antenna sets of the cell, delay module 601 isadvantageously employed to ensure the appropriate transmission delaybetween the signals being transmitted by antenna sets 13, 15 and 17.Delay module 601 is constructed in a manner well-known to those skilledin the art. Delay module 601 is shown comprising time delay circuits foreach of the three zone sites. However, those skilled in the art willrecognize that the number of required delay circuits corresponds to thenumber of transmitting antenna, minus one. Corresponding delay modules602 and 603 are employed to delay the signals arriving from the zonecites. These modules allow correlation and combination of signalstransmitted from the mobile unit in the cell to the three antenna sets.Those skilled in the art will recognize that modules 601-603 may beplaced in other locations in the reception and transmission lines andmay include or work in conjunction with correlator and/or combinermodules.

Various modifications of the invention, in addition to those shown anddescribed herein, will be apparent to those skilled in the art from theforegoing description and accompanying drawings. Such modifications areintended to fall within the scope of the appended claims.

What is claimed is:
 1. A method of operating a cellular telephone systemcomprised of a plurality of cells, each of the cells being comprised ofa plurality of zones, each of the zones having at least one antennasuitably arranged and positioned therein and configured to limitpropagation of radio frequency (RF) signals radiated from the antenna tosubstantially within pre-defined boundaries of the zone, each of thecells having an assigned set of identification codes, and each of theidentification codes being used to encode radio frequency (RF) signalscommunicated to a mobile telephone within the cell, the methodcomprising:(a) transmitting and receiving the RF signals at assignedfrequencies to communicate with mobile telephones within the zone,wherein a plurality of the mobile telephones simultaneously use anidentical assigned frequency and a different one of the identificationcodes assigned to the cell; (b) maintaining communications with themobile telephones by activating and deactivating transmissions to themobile telephones as they move from zone to zone while using the sameidentification codes for each of the mobile telephones; and (c)maintaining communications with the mobile telephones by changing theidentification codes for each of the mobile telephones as they move fromcell to cell.
 2. The method as set forth in claim 1 above, wherein theantenna is located on a periphery of the zone and is pointed into acenter of the zone to substantially limit propagation of signals to thezone.
 3. The method as set forth in claim 1 above, wherein the zones arearranged in a manner to create linear coverage for the cell.
 4. Themethod as set forth in claim 1 above, further comprising the stepsof:monitoring one or more characteristics of a signal received by theantenna; and terminating transmissions in all zones except for a zoneselected on the basis of the monitored signal characteristic.
 5. Themethod as set forth in claim 1 above, further comprising the stepsof:receiving a signal from mobile transmitters within the zone at areceiver coupled to the antenna; measuring a characteristic of thereceived signal; and activating and deactivating one or moretransmitters in the zones according to the measured characteristic. 6.The method as set forth in claim 1 above, wherein transmissions ofsignals to a particular mobile phone in each of the zones occurs on thesame frequency, thereby eliminating handoffs between zones.
 7. Themethod as set forth in claim 1 above, further comprising connecting abase site to the antenna in the zone.
 8. The method as set forth inclaim 7 above, further comprising the steps of converting signals at thebase site from a cellular phone frequency to a microwave frequency,transmitting the signals from the base site to the zone, and convertingthe signals at the zone from the microwave frequency to the cellularphone frequency.
 9. The method as set forth in claim 7 above, furthercomprising the steps of converting signals at the base site from acellular phone frequency to an optical frequency, transmitting thesignals from the base site to the zone, and converting the signals atthe zone from the optical frequency to the cellular phone frequency. 10.An antenna system for a cellular telephone system, wherein the cellulartelephone system comprises a plurality of cells, each of the cells beingcomprised of a plurality of zones, each of the cells having an assignedset of identification codes, and each of the identification codes beingused to encode radio frequency (RF) signals communicated to a mobiletelephone within the cell, comprising:at least one antenna suitablyarranged and positioned within each zone and configured to limitpropagation of radio frequency (RF) signals radiated therefrom tosubstantially within pre-defined boundaries of the zone, wherein theantenna is coupled to a means for transmitting and receiving the RFsignals at assigned frequencies to communicate with mobile telephoneswithin the zone, wherein a plurality of the mobile telephonessimultaneously use an identical assigned frequency and a different oneof the identification codes assigned to the cell, and wherein the meansfor transmitting and receiving further comprises means for maintainingcommunications with the mobile telephones by activating and deactivatingtransmissions to the mobile telephones as they move from zone to zonewhile using the same identification codes for each of the mobiletelephones and means for maintaining communications with the mobiletelephones by changing the identification codes for each of the mobiletelephones as they move from cell to cell.
 11. The antenna system as setforth in claim 10 above, wherein the antenna is located on a peripheryof the zone and is pointed into a center of the zone to substantiallylimit propagation of signals to the zone.
 12. The antenna system as setforth in claim 10 above, wherein the zones are arranged in a manner tocreate linear coverage for the cell.
 13. The antenna system as set forthin claim 10 above, wherein the means for transmitting and receivingfurther comprises:means for monitoring one or more characteristics of asignal received by the antenna; and means for terminating transmissionsin all zones except for a zone selected on the basis of the monitoredsignal characteristic.
 14. The antenna system as set forth in claim 10above, wherein the means for transmitting and receiving furthercomprises:means for receiving a signal from mobile transmitters withinthe zone; means for measuring a characteristic of the received signal;and means for activating and deactivating one or more transmitters inthe zones according to the measured characteristic.
 15. The antennasystem as set forth in claim 10 above, wherein transmissions of signalsto a particular mobile phone in each of the zones occurs on the samefrequency, thereby eliminating handoffs between zones.
 16. The antennasystem as set forth in claim 10 above, further comprising means forconnecting a base site to the antenna in the zone.
 17. The antennasystem as set forth in claim 16 above, further comprising means forconverting signals at the base site from a cellular phone frequency to amicrowave frequency, for transmitting the signals from the base site tothe zone, and for converting the signals at the zone from the microwavefrequency to the cellular phone frequency.
 18. The antenna system as setforth in claim 16 above, further comprising means for converting signalsat the base site from a cellular phone frequency to an opticalfrequency, for transmitting the signals from the base site to the zone,and for converting the signals at the zone from the optical frequency tothe cellular phone frequency.